"It's a new setback but we are cautiously optimistic about his prognosis. With that said, we understand the seriousness of this disease.

"Mr. Hughes is committed to always doing what's best for the horse, and that means Lord Nelson will be withheld from breeding mares this season. Our team has notified all of the breeders from his full book, and our focus is now 100 per cent on bringing him back to good health. We very much appreciate the breeders for their understanding."

The five-year-old son of Pulpit was trained by Bob Baffert and captured three consecutive Grade 1 wins in 2016 for Spendthrift. He beat the track record over 6f in the Bing Crosby Stakes at Del Mar in the summer and won both the Triple Bend Stakes and the Santa Anita Sprint Championship. Lord Nelson was an early favourite for the Breeders' Cup Sprint at Santa Anita before incurring a leg infection that forced his trainer to scratch him and retire him from racing.

Out of the Seeking the Gold mare African Jade, Lord Nelson had been fully booked for his first breeding season in 2017 at a fee of $25,000.